Vietnam has a tropical monsoon climate, with humidity averaging 84 percent throughout the year. However, because of differences in latitude and the marked variety of topographical relief, the climate tends to vary considerably from place to place. During the winter or dry season, extending roughly from November to April, the monsoon winds usually blow from the northeast along the China coast and across the Gulf of Tonkin, picking up considerable moisture; consequently the winter season in most parts of the country is dry only by comparison with the rainy or summer season. During the southwesterly summer monsoon, occurring from May to October, the heated air of the Gobi Desert rises, far to the north, inducing moist air to flow inland from the sea and deposit heavy rainfall.

Annual rainfall is substantial in all regions and torrential in some, ranging from 120 centimeters to 300 centimeters. Nearly 90 percent of the precipitation occurs during the summer. The average annual temperature is generally higher in the plains than in the mountains and plateaus. Temperatures range from a low of 5°C in December and January, the coolest months, to more than 37°C in May-July, the hottest months. Seasonal divisions are more clearly marked in the northern half than in the southern half of the country, where, except in some of the highlands, seasonal temperatures vary only a few degrees, usually in the 21°C-28°C range.

In the North, a hot rainy season prevails from May through September. The average temperature in Ha Noi is about 33C during this period, with very high humity. At times heavy summer rains cause some sections of the city to flood temporarily due to the lack of proper drainage.

From September through November, it's supposed to be Aumtumn in the North. But nowaways it could be anything from perfect nice, dry and breezy weather to stormy and monsoonal. The average temperature during this time is 25C-28C.

During the cooler, dry season in the North from December to March, the average temperature is 15C, with overnight minimums sometimes around 6-8C. Due to the lack of heating in most shops and offices during the dry season, it will feel considerably colder.

The rainy season in Da Nang and Hue in the centre of the country lasts from September to February. Whenever it rains, things are gloomy and cool in Hue and Da Nang. From February through April it's pleasant with breezy weather. From May to September it may get up to 36-37C around this area.

In the South, Ho Chi Minh City and the Mekong Delta experience a year-round hot and humid tropical climate with daily temperatures normally exceeding 33C. The rainy season lasts from April/May to November, with heavy rains for 30 minutes/day which refresh the atmosphere of oppressive heat.